cmd/link: fix StackCheckOutput on AIX

This test forces GOARCH to amd64, but currently uses the default GOOS.
This works on every OS that supports amd64, which is every OS we
support except AIX. Hence, on AIX this fails with an unsupported
GOOS/GOARCH combination.

Fix this by forcing GOOS to linux.

Fixes #52451.

Change-Id: I9321dd6386c7ef0fe2b47d77ed900aafc53f2a46
Reviewed-on: https://go-review.googlesource.com/c/go/+/401334
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Austin Clements <austin@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/cmd/link/internal/ld/stackcheck.go

@@ -101,7 +101,7 @@ func (ctxt *Link) doStackCheck() {
 		// the same function multiple times at different
 		// depths, but lets us find all paths.
 		for _, root := range roots {
-			ctxt.Errorf(root, "nosplit stack overflow")
+			ctxt.Errorf(root, "nosplit stack over %d byte limit", limit)
 			chain := []stackCheckChain{{stackCheckEdge{0, root}, false}}
 			sc.report(root, limit, &chain)
 		}

src/cmd/link/internal/ld/stackcheck_test.go

@@ -5,13 +5,12 @@
 package ld
 
 import (
-	"cmd/internal/objabi"
-	"cmd/internal/sys"
 	"fmt"
 	"internal/testenv"
 	"os"
 	"os/exec"
 	"regexp"
+	"strconv"
 	"testing"
 )
 
@@ -24,7 +23,7 @@ func TestStackCheckOutput(t *testing.T) {
 	cmd := exec.Command(testenv.GoToolPath(t), "build", "-o", os.DevNull, "./testdata/stackcheck")
 	// The rules for computing frame sizes on all of the
 	// architectures are complicated, so just do this on amd64.
-	cmd.Env = append(os.Environ(), "GOARCH=amd64")
+	cmd.Env = append(os.Environ(), "GOARCH=amd64", "GOOS=linux")
 	outB, err := cmd.CombinedOutput()
 
 	if err == nil {
@@ -34,13 +33,13 @@ func TestStackCheckOutput(t *testing.T) {
 
 	t.Logf("linker output:\n%s", out)
 
-	// Construct expected stanzas
-	arch := sys.ArchAMD64
-	call := 0
-	if !arch.HasLR {
-		call = arch.RegSize
+	// Get expected limit.
+	limitRe := regexp.MustCompile("nosplit stack over ([0-9]+) byte limit")
+	m := limitRe.FindStringSubmatch(out)
+	if m == nil {
+		t.Fatalf("no overflow errors in output")
 	}
-	limit := objabi.StackLimit - call
+	limit, _ := strconv.Atoi(m[1])
 
 	wantMap := map[string]string{
 		"main.startSelf": fmt.Sprintf(
@@ -67,7 +66,7 @@ func TestStackCheckOutput(t *testing.T) {
 	}
 
 	// Parse stanzas
-	stanza := regexp.MustCompile(`^(.*): nosplit stack overflow\n(.*\n(?: .*\n)*)`)
+	stanza := regexp.MustCompile(`^(.*): nosplit stack over [0-9]+ byte limit\n(.*\n(?: .*\n)*)`)
 	// Strip comments from cmd/go
 	out = regexp.MustCompile(`(?m)^#.*\n`).ReplaceAllString(out, "")
 	for len(out) > 0 {